This disclosure relates generally to biasing semi-conductor wells, and more particularly to controlling semiconductor well biasing.
As semiconductor processes advance, the size of the devices that can be constructed on a semiconductor substrate continues to grow smaller. With the reduction in device sizes comes corresponding reductions in gate oxide thicknesses, and lowered threshold voltage requirements. In addition, as device sizes shrink, the problem with current leaking between devices, and between various device features, is exacerbated. Limiting device leakage currents is important, especially in hand-held, battery-operated products where power consumption often dictates product success. Since many handheld products are typically not used for significant periods of timexe2x80x94up to 95% of the time for some products controlling the current leakage of semiconductor devices during periods when the product is not in use can result in reduced power consumption.
One method of reducing the leakage current of a semiconductor device is to increase the voltage needed to turn the transistors of the device on. For example, when a complimentary metal oxide semiconductor (CMOS) transistor is to be turned on, enough voltage must be supplied at the gate of the CMOS transistor to allow current to flow between the transistor""s source and drain. The amount of voltage needed is called the threshold voltage. In order to ensure that current does not leak between the CMOS transistor""s source and drain when the transistor is not in use, a well bias circuit, or charge pump, is used to increase the transistor""s threshold voltage. As a result of the increased threshold voltage, the leakage current between the transistor""s source and drain can be reduced or eliminated.
However, the well bias circuit uses some amount of current for its own operation and there are cases in which the amount of current used by the well bias circuit is greater than the amount of leakage current that would occur if no well bias circuit were used. As a result, use of the well bias circuit may, in some cases, actually increase the overall amount of current used by the consumer product, thereby shortening battery life.
What is needed, therefore, is a way to decrease the total current used by a product, regardless of whether the current is being leaked by a semi-conductor device within the product, or whether the current is being consumed by a well bias circuit.